Stink Bugs Could Still Be A Problem In Soybeans
Dr. Doug Johnson
PRINCETON, KY.
Because of delayed planting and a cool summer, Kentucky soybean
producers are likely to have considerable acreage of late maturing
soybeans. This probably causes most folks to be concerned with frost.
However, this extended maturity may also set up fields for additional
damage by stink bugs. Producers and consultants should remain watchful
as long as pods are still filling.
By far, the most common stink bug found in Kentucky is the green stink
bug (Figure 1). Our research indicates that green stink bugs make up
greater than 80 percent of the population. Nonetheless, there are
several species of brown stinkbugs (Figure 2) in Kentucky-grown beans as
well. So expect to see both types.
Stink bugs can cause decreases in both yield and seed quality. These
pesky bugs feed directly on the bean using their piercing-sucking mouth
parts. They puncture the pod wall and stab the developing bean, removing
nutrients and sometimes allowing entrance of pathogens into the pod /
bean. Usually, there is no clear evidence of this damage until the pods
are mature. The only clear evidence one has of these important pests is
observing them in the field; damage symptoms are too late.
Stink bugs will hang around until frost, feeding on whatever is
available to them. In soybeans we consider the pods at risk up through
to R6 stage. So if you have beans less mature than this you should
definitely be looking for these critters. Once soybeans are in the R6
stage stink bug damage is much more difficult to predict.
Sampling for the pest can be done in two ways. In wide row beans a shake
cloth (aka = drop cloth) may be used. This is a 3- foot long section of
white cloth wide enough to reach from row to row. Shake the beans on
both sides over the cloth and count the stink bugs that fall to the
cloth. Remember, adults can fly so you need to count quickly. Juveniles
do not yet have wings so they are a bit slower to escape. In narrow row
beans you will need to use a sweep net. The 15-inch-diameter sweep net
is the standard tool for most thresholds. Take 25 sweeps per location
and count the stink bugs captured. In both types of sampling, each field
should be sampled at multiple locations. The more locations you sample,
the more accurate and precise your estimates will be. Average the
number of stink bugs captured over all locations.
Thresholds that warrant control are: shake cloth – an average of one
stink bug per row foot, or if sampled with a sweep net, treat if you
collect an average of 9 stinkbugs per 25 sweeps at R4-R6.
If control is required, synthetic pyrethroid insecticides are commonly
used for control and are very effective on green stink bugs. Brown stink
bugs are a bit more tolerant of pyrethroids, so if they are plentiful,
inclusion of an organophosphate like acephate may be needed.
Insecticides for use against this pest in soybeans may be found at: http://pest.ca.uky.edu/EXT/Recs/welcomerecs.html.
Producers in the central and eastern Kentucky production areas also need
to keep their eyes open for the two invasive stink bug species resident
in Kentucky. Populations of the brown marmorated stink bug (BMSB) have
become established in central and eastern Kentucky over the last 3
years. BMSBs look typically like other brown stink bugs except that they
are often a bit larger and have two small but very distinct white bands
surrounding the joints in their antennae (Figure 3).
In addition, the Kudzu bug has been found in three southeastern Kentucky
counties bordering I-75. They are dark green to olive with a rounded
shape and about the size of an English pea (Figure 4).
Neither of these species is believed to be of major importance in this
year’s crop, but as their populations become established and grow larger
in size they have the potential to become major soybean pests. Any
interested party that has collected what is believed to be a BMSB or
Kudzu bug is asked to submit the insect to their county Cooperative
Extension Office for identification.∆
DR. DOUG JOHNSON: Extension Entomologist, University of Kentucky